ob-sql.el: Enhance postgresql support

* lisp/ob-sql.el (org-babel-sql-dbstring-postgresql): New function
  (org-babel-execute:sql): Use new function.

Before this patch, it was necessary to use :cmdline parameter to
specify host, user and database different the the default ones.  Now,
this can be done using parameters that are independents of the engine
used.

This is not trivial (and not recommended) to pass password as a
command line argument to psql, so :dbpassword is not supported.

lisp/ob-sql.el

@@ -87,6 +87,15 @@
 	       (when password (concat "-p" password))
 	       (when database (concat "-D" database))))))
 
+(defun org-babel-sql-dbstring-postgresql (host user database)
+  "Make PostgreSQL command line args for database connection.
+Pass nil to omit that arg."
+  (combine-and-quote-strings
+   (delq nil
+	 (list (when host (concat "-h" host))
+	       (when user (concat "-U" user))
+	       (when database (concat "-d" database))))))
+
 (defun org-babel-execute:sql (body params)
   "Execute a block of Sql code with Babel.
 This function is called by `org-babel-execute-src-block'."
@@ -123,8 +132,9 @@ This function is called by `org-babel-execute-src-block'."
 				    (org-babel-process-file-name in-file)
 				    (org-babel-process-file-name out-file)))
 		    ('postgresql (format
-				  "psql --set=\"ON_ERROR_STOP=1\" %s -A -P footer=off -F \"\t\"  -f %s -o %s %s"
+				  "psql --set=\"ON_ERROR_STOP=1\" %s -A -P footer=off -F \"\t\"  %s -f %s -o %s %s"
 				  (if colnames-p "" "-t")
+				  (org-babel-sql-dbstring-postgresql dbhost dbuser database)
 				  (org-babel-process-file-name in-file)
 				  (org-babel-process-file-name out-file)
 				  (or cmdline "")))